CENOZOIC VOLCANISM IN ANTARCTICA - JONES MOUNTAINS AND PETER-I ISLAND

Cenozoic volcanism is widespread along the Pacific coast of Antarctica ; a relationship to the rifting of the West Antarctic Rift System is o bvious, but the possible role for mantle plumes is not established. We compare here complete geochemical and strontium, neodymium, and lead isotopic data for volcanic rocks from one probable plume just off the coast of Ellsworth Land (Peter I Island) with data from rift-related v olcanic rocks from the nearby Jones Mountains, Ellsworth Land. The alk ali basalts from Peter I Island are similar in most respects to averag e oceanic island basalt, and we propose recognition of this island as the most southerly known oceanic plume/hotspot -only unusually high Pb -207/204 ratios set the Peter I Island plume apart from other oceanic plumes. The volcanics from the Jones Mountains share many trace elemen t and isotopic characteristics with the Peter I volcanics, including i sotopic arrays which have as one end member the low Sr-87/86-high Pb-2 06/204 component which is characteristic of Cenozoic volcanism through out the West Antarctic Rift System. Basalts from the Jones Mountains a re distinctive from those of Peter I island principally in their much lower(207/204)Pb ratios, and their low and non-OIB-like Ce/Pb ratios ( 8.5-17.6). To explain this difference, we propose that a minor compone nt of subduction-impregnated subcontinental lithosphere has been incor porated into the rift-related Jones Mountains volcanics that is not pr esent in the oceanic Peter I Island plume.